The group behind the calls is American Freedom Party (AFP), a white supremacist group that endorsed the Republican candidate on Friday, calling him their "Great White Hope."

"We don't need Muslims. We need smart, well-educated white people who will assimilate to our culture. Vote Trump," Jared Taylor, a white nationalist and editor of the supremacist magazine American Renaissance, says on the call.

The robocall campaign is paid for by the American National super PAC, led by the AFP, which Dylann Roof, the man who killed nine people in a shooting at a historically black church in Charleston, cited as his inspiration.

The robocall, which has drawn more attention, and contention, to Mr. Trump's candidacy, underscores how racially charged the presidential contest, and particularly the Republican race, has become.

Arguably, that's largely thanks to Trump, who emerged as a surprise front-runner by tapping into some voters' fears and anger. He declared his candidacy in a speech denouncing Mexican immigrants as "rapists" and "criminals" and has used his campaign to stake a series of controversial positions, including forcibly deporting 11 million undocumented immigrants and temporarily banning all Muslims from entering the United States.

To be clear, Trump does not endorse white supremacist groups, and two staffers were fired from his campaign for posting racially offensive material on social media.

His comments appear to have roused white supremacist groups, for whom Trump is a mainstream candidate who shares, and loudly asserts, many of their decidedly non-mainstream views.

"Clearly our movement has been energized by Trump," Richard Spencer, director of the National Policy Institute, a far-right group dedicated to promoting the interests of white Americans, told Reuters.

"I think what he's done is a very important thing," Mr. Taylor told The Washington Post. "He's the first candidate in decades to say almost explicitly that immigration should be in the interest of Americans and not just immigrants."

"He's attractive to many Americans who see their country slipping through their fingers," he added. "You don't want to end your days living in an outpost of Haiti or Guatemala do you?"

The unsolicited support – former KKK Grand Wizard David Duke also recently endorsed Trump – puts the candidate in a delicate position.

When Bloomberg asked him about the public endorsement from Mr. Duke, who ran for the GOP nomination in 1992, Trump responded, "I don’t need his endorsement; I certainly wouldn’t want his endorsement. I don’t need anyone’s endorsement.” When asked if he would repudiate Duke’s support, Trump replied: “Sure, I would if that would make you feel better.”

But he didn't appear to be particularly distressed about it, either, adding, "People like me across the board. Everyone likes me."